Dynamic Duo Confronts Refrigerator Menace

"The Einstein-Szilard Refrigerators" by Gene Dannen, in Scientific American (Jan. 1997), 415 Madison Ave., New York, N.Y. 10017–1111.

In July 1939, Albert Einstein and Hungarian-born physicist Leo Szilard met to ponder the news that scientists had produced a fission reaction in uranium. As a result, Einstein wrote his famous letter to President Franklin D. Roosevelt warning that Nazi Germany might be able to develop nuclear weapons. That, notes Dannen, an independent scholar, was not the first time Einstein and Szilard had collaborated for the benefit of mankind. A decade earlier, they had worked to avert the danger posed by mechanical home refrigerators.

Einstein, who by the mid-1920s was the world’s most renowned physicist, became interested in the problem when he read of an entire family that had been killed by toxic gases leaking from their refrigerator.

Refrigerators then, as now, used mechanical compressor motors to compress a refrigerant gas, which then liquefies as excess heat is discharged. When the liquid is allowed to expand again, it cools and can absorb heat from an interior chamber.

But the early refrigerants were toxic, and leaks were inevitable in systems with moving parts. The two physicists’ solution: a cooling system that did not involve mechanical motion and so did not require moving parts.

Swedish inventors had designed a socalled absorption refrigerator—in which heat from a natural gas flame, rather than the push of a piston, drives the cooling cycle—and the Swedish firm AB Electrolux was marketing it. Szilard and Einstein devised an improvement—and came up with a host of other designs. In early 1926, Szilard began filing patent applications, and by the fall, he and Einstein had decided on the three most promising designs. One, based on absorption, was very similar to the Electrolux machine; a second was based on the principle of diffusion. Electrolux, seeking mostly to safeguard its own pending patent applications, bought both those designs but never developed either one.

The physicists’ third design turned out to be their "most revolutionary, and most successful, invention": an electromagnetic pump. In it, Dannen explains, "a traveling electromagnetic field caused a liquid metal to move. The metallic fluid, in turn, was used as a piston to compress a refrigerant." Although less efficient than standard compressors and very noisy, the pump would not leak or fail. In July 1931, an Einstein-Szilard refrigerator went into continuous operation at a Berlin manufacturer’s research institute.

But the growing worldwide depression and improvements in conventional refrigerators truncated the experimental refrigerator’s career. In 1930, Americans demonstrated a new nontoxic refrigerant called Freon, which soon became the global standard. Two years later, the Berlin firm, hit hard by the depression, killed the refrigerator project.

Although the two physicists never produced a product that reached the consumer market, Dannen writes, the Einstein-Szilard pump eventually proved its value: "The built-in safety of its design later found a more critical task in cooling breeder reactors."